Method for producing bisphenol-A

ABSTRACT

Provided is a process for producing a bisphenol A by continuously feeding phenol and acetone into a reactor unit having at least two reaction zones connected in series. In the process, an acidic cation-exchange resin partially neutralized with a sulfur-containing nitrogen compound in from 15 to 50% of the acid site thereof is used as the catalyst, and acetone having a methanol concentration of at most 3,000 ppm is separately fed into at least two reaction zones in the reactor unit. The life of the acidic cation-exchange resin catalyst used in the process is prolonged.

TECHNICAL FIELD

The present invention relates to a process for producing bisphenol A inwhich the life of the catalyst, acidic cation-exchange resin used can beprolonged. Bisphenol A is useful as a material for polycarbonate resin,epoxy resin, polyarylate resin, etc.

BACKGROUND ART

Bisphenol A [2,2-bis(4-hydroxyphenyl)propane] is known to be animportant compound for a material for engineering plastics such aspolycarbonate resin and polyarylate resin or for epoxy resin, and thereis increasing a great demand for it these days.

It is known that bisphenol A is produced by condensing acetone andexcess phenol in the presence of an acidic cation-exchange resincatalyst and optionally a sulfur compound promoter such asalkylmercaptan. In the process, the acidic cation-exchange resincatalyst degrades with time. A principal cause of the catalystdegradation is the heavy material derived from the starting compounds,and the catalyst begins to degrade first around the inlet port of thereactor. Since its degradation speed is high, an excess amount of thecatalyst is charged into the reactor for long-term continuous operationfor bisphenol A production. After the catalyst has begun to degrade, theamount of acetone to be fed into the reactor must be time-dependentlyincreased for keeping the product yield (that is, for keeping theintended degree of phenol conversion). In that case, the non-reactedacetone that goes out of the reactor is recovered in the distillationcolumn connected to the outlet port of the reactor. Therefore, theamount of acetone that maybe increased in the process is limited by thecapacity of the distillation column. That is, at the limit of thecapacity of the distillation column, the catalyst in the reactor isexchanged with a fresh one. Accordingly, if the reaction condition couldbe suitably controlled so as not to increase the amount of acetone andso as to use the catalyst as long as possible in the reactor, it willreduce the production costs. In this connection, some patentapplications relating to improvement of the reaction condition have beenlaid open to public inspection, though their objects differ. Forexample, Japanese Patent Laid-Open No. 19952/1979, Japanese Patent No.2,779,952, Japanese Patent Laid-Open No. 246458/1999 and U.S. Pat. No.4,400,555 disclose a specific arrangement of reactors connected inseries in which a carbonyl compound divided into some portions is addedseparately to each reactor. In these, however, there is still room forimprovement for prolonging the life of the acidic cation-exchange resinused.

The present invention has been made in consideration of theabove-mentioned matters, and its object is to provide a process forproducing bisphenol A in which the life of the catalyst, acidiccation-exchange resin used can be prolonged.

DISCLOSURE OF THE INVENTION

We, the present inventors have assiduously studied, and, as a result,have found that, in a process of producing bisphenol A by continuouslyfeeding phenol and acetone into a reactor unit having at least tworeaction zones connected in series, when an acidic cation-exchange resinthat has been specifically partially neutralized is used as the catalystand when acetone having a specific methanol concentration is separatelyfed into at least two reaction zones in the reactor unit, then theprocess ensures a high degree of phenol conversion. On the basis of thisfinding, we have completed the present invention.

Specifically, the invention provides a process for producing a bisphenolA by continuously feeding phenol and acetone into a reactor unit havingat least two reaction zones connected in series, which is characterizedin that an acidic cation-exchange resin partially neutralized with asulfur-containing nitrogen compound in from 15 to 50% of the acid sitethereof is used as the catalyst, and acetone having a methanolconcentration of at most 3,000 ppm is separately fed into at least tworeaction zones in the reactor unit.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows one example of a flowchart of reaction steps of the processof the invention. A indicates acetone; B indicates phenol; 1 indicates afirst reactor; 2 indicates a second reactor; and 3 indicates a thirdreactor.

BEST MODES OF CARRYING OUT THE INVENTION

The invention is described in detail hereinunder.

First described is the outline of the steps of the process for producingbisphenol A of the invention.

Step (1) (Reaction Step)

Bisphenol A is produced by reacting acetone with excess phenol in thepresence of an acidic cation-exchange resin catalyst and optionally analkylmercaptan serving as a promoter. For the acidic cation-exchangeresin catalyst, generally preferred is a sulfonic acid-typecation-exchange resin. For example, it includes sulfonatedstyrene-divinylbenzene copolymer, sulfonated crosslinked styrenepolymer, phenol-formaldehyde-sulfonic acid resin, andbenzene-formaldehyde-sulfonic acid resin. Singly or as combined, one ormore of these may be used as the catalyst.

In addition to the product bisphenol A therein, the reaction mixturecontains non-reacted phenol, non-reacted acetone, catalyst, by-producedwater, alkylmercaptan, as well as side products such as organic sulfurcompounds and color substances.

Step (2) (Step of Recovering By-produced Water and Non-reactedCompounds)

Next, the reaction mixture obtained in the step (1) is distilled underreduced pressure, whereby the non-reacted acetone, by-produced water andalkylmercaptan are removed through the top of the distillation columnand a liquid mixture that contains bisphenol A and phenol is taken outthrough the bottom thereof. The condition for the reduced-pressuredistillation in this step is as follows: The pressure falls between 7and 80 kPa, and the temperature falls between 70 and 180° C. In thatcondition, the non-reacted phenol forms an azeotrope and a part of it isremoved out of the system through the top of the distillation column.

Step (3) (Step of Condensing Bisphenol A)

The bottom liquid of the reaction mixture from which the substances asabove have been removed is then distilled under reduced pressure toremove phenol from it, and the product bisphenol A is thereby condensed.The resulting condensate residue is crystallized in the next step. Thecondensation condition is not specifically defined. In general, thetemperature falls between 100 and 170° C., and the pressure fallsbetween 5 and 67 kPa. If the temperature is lower than 100° C., thecondensation will require high vacuum; but if higher than 170° C., thenext crystallization step will require an additional treatment for heatremoval. The bisphenol A concentration of the condensate residue mayfall between 20 and 50% by mass, but preferably between 20 and 40% bymass. If the concentration is lower than 20% by mass, the bisphenol Arecovery will be low; but if higher than 50% by mass, the slurrytransfer after crystallization will be difficult.

Step (4) (Crystallization Step)

The condensate residue obtained in the step (3) is cooled to 40 to 70°C. to give a crystal of bisphenol A-phenol adduct (hereinafter this isabbreviated as phenol adduct), and it becomes slurry. Cooling theresidue may be effected by applying water to the external heat exchangeror crystallizer fitted to the reactor unit for heat removal from theresidue through vaporization of water. Next, the condensate residueslurry is filtered or centrifuged to separate the phenol adduct from thecrystal-free mother liquid that contains side products. The motherliquid is directly or partly recycled into the reactor unit, or apart orall of it is decomposed with alkali into phenol and isopropenylphenoland they are recovered. As the case may be, a part or all of the motherliquid may be isomerized and recycled to crystallization.

Step (5) (Step of Heating and Melting Phenol Adduct)

The crystal of 1:1 adduct of bisphenol A and phenol obtained in the step(4) is melted under heat at 100 to 160° C. into a liquid mixture.

Step (6) (Step of Recovering Bisphenol A)

Through distillation under reduced pressure, phenol is removed from theliquid mixture obtained in the step (5), and bisphenol A is thusrecovered. The condition of the reduced-pressure distillation is asfollows: The pressure falls between 1 and 14 kPa; and the temperaturefalls between 150 and 190° C. Apart from such treatment, another methodof removing the remaining phenol through steam stripping is also known.

Step (7) (Step of Granulating Bisphenol A)

The bisphenol A obtained in melt in the step (6) is formed into liquiddrops in a granulator such as spray drier, then cooled and solidified.This is the final product of the invention. The liquid drops are formedby spraying or sprinkling the melt and then cooled by exposing them tonitrogen or air.

Next, the process of the invention is described in detail.

The process of the invention is for producing bisphenol A bycontinuously feeding phenol and acetone into a reactor unit having atleast two reaction zones connected in series, and is characterized inthat an acidic cation-exchange resin partially neutralized with asulfur-containing nitrogen compound in from 15 to 50% of the acid sitethereof is used as the catalyst, and acetone having a methanolconcentration of at most 3,000 ppm is separately fed into at least tworeaction zones in the reactor unit.

Specifically in the process the catalyst to be used is an acidiccation-exchange resin partially neutralized with a sulfur-containingnitrogen compound in from 15 to 50% of the acid site thereof. If thedegree of neutralization of the cation-exchange resin used as thecatalyst in the process is lower than 15%, the catalyst will lose themethanol resistance of itself and the separate addition of acetone todifferent reactors will be ineffective. If higher than 50%, on the otherhand, it is unfavorable since the catalyst activity greatly lowers.Preferably, the degree of neutralization of the catalyst falls between20 and 30%.

The sulfur-containing nitrogen compound to be used for the catalystneutralization includes, for example, pyridinealkanethiols such as3-mercaptomethylpyridine, 3-mercaptoethylpyridine,2-mercaptoethylpyridine, 4-mercaptoethylpyridine;pyridylalkanethioacetals to be obtained from such pyridinealkanethiolswith ketones such as acetone, methyl ethyl ketone, methyl isobutylketone, acetophenone, cyclohexanone; aminoalkanethiols such as2-mercaptoethylamine, 3-mercaptobutylamine,3-n-propylamino-1-propylmercaptan; and thiazolidines such asthiazolidine, 2,2-dimethylthiazolidine, cycloalkylthiazolidines. Aboveall, preferred are 2,2-dimethylthiazolidine and 2-mercaptoethylamine.

In the process, it is also indispensable that the methanol concentrationof acetone is at most 3,000 ppm. If higher than 3,000 ppm, it isunfavorable since the influence of methanol on the process is too great.Preferably, the methanol concentration is at most 2,000 ppm.

The reaction temperature preferably falls between 60 and 100° C. Iflower than 60° C., it is unfavorable since the phenol phase willsolidify; but if higher than 100° C., it is also unfavorable since theion-exchange resin used will be too much degraded. More preferably, thereaction temperature falls between 65 ad 95° C.

Also preferably, the ratio (by mol) of phenol/total acetone fallsbetween 6 and 13. If smaller than 6, it is unfavorable since the colorof the product, bisphenol A will be unstable; but if higher than 13, itis also unfavorable since the reaction speed will be low and the amountof phenol to be recovered will increase. More preferably, the ratiofalls between 8 and 12.

The amount of acetone to be fed into each reactor is not specificallydefined. For example, from 30 to 50% of all acetone to be fed into thereactor unit may be fed into the first reactor, and the remainingacetone is divided into equal parts and equally fed into the second andlater reactors. FIG. 1 is a flowchart showing one example of theinvention that uses a three-stage reactor unit.

Preferably, the liquid hourly space velocity (LHSV) in each reactorfalls between 0.2 and 30 hr⁻¹, more preferably between 0.5 and 6 hr⁻¹.

The invention is described more concretely with reference to thefollowing Examples, which, however, are not intended to restrict thescope of the invention.

EXAMPLE 1

69 cc of an acidic cation-exchange resin neutralized with2,2-dimethylthiazolidine in 20% of the acid site thereof (MitsubishiChemical's Diaion SK104) was, after swollen with water, charged intoeach of three stainless columns. 277 cc/hr of phenol and 8 cc/hr ofacetone were fed into the reactor unit through the inlet port of eachreactor column. The reaction temperature in the unit was kept at 75° C.The ratio (by mol) of phenol/all acetone was 10. The methanolconcentration of the acetone was 1,000 ppm. In the initial stage ofreaction, the phenol conversion at the outlet port of the third reactorcolumn was 14.0%, and after 500 hours, it was 12.8%.

COMPARATIVE EXAMPLE 1

In the same reactor unit as in Example 1, all acetone was fed into thefirst reactor column at a flow rate of 24 cc/hr, and reacted with phenolin the same manner as in Example 1. In the initial stage of reaction,the phenol conversion at the outlet port of the third reactor column was14.0%, but after 500 hours, it was 12.0%. There is a significantdifference between the data, 12.8% in Example 1 and 12.0% in ComparativeExample 1.

COMPARATIVE EXAMPLE 2

In the same reactor unit as in Example 1, an ion-exchange resin having adegree of neutralization of 10% was used and acetone and phenol werereacted in the same manner as in Example 1. In the initial stage ofreaction, the phenol conversion at the outlet port of the third reactorcolumn was 14.0%, but after 500 hours, it was 11.2%.

COMPARATIVE EXAMPLE 3

In the same reactor unit as in Example 1, acetone having a methanolconcentration of 5,000 ppm was reacted with phenol in the same manner asin Example 1. In the initial stage of reaction, the phenol conversion atthe outlet port of the third reactor column was 14.0%, but after 500hours, it was 11.8%.

INDUSTRIAL APPLICABILITY

In the process of the present invention for producing a bisphenol A bycontinuously feeding phenol and acetone into a reactor unit having atleast two reaction zones connected in series, an acidic cation-exchangeresin partially neutralized with a sulfur-containing nitrogen compoundin from 15 to 50 of the acid site thereof is used as the catalyst, andacetone having a methanol concentration of at most 3,000 ppm isseparately fed into at least two reaction zones in the reactor unit. Theadvantage of the process of producing bisphenol A is that the life ofthe acidic cation-exchange resin catalyst used is prolonged.

1. A process for producing a bisphenol A by continuously feeding phenoland acetone into a reactor unit having at least two reaction zonesconnected in series, which is characterized in that an acidiccation-exchange resin partially neutralized with a sulfur-containingnitrogen compound in from 15 to 50% of the acid site thereof is used asthe catalyst, and acetone having a methanol concentration of from 1,000to 3,000 ppm is separately fed into at least two reaction zones in thereactor unit.
 2. The process for producing bisphenol A as claimed inclaim 1, wherein the ratio (by mol) of phenol/all acetone falls between6 and
 13. 3. The process for producing bisphenol A as claimed in claim1, wherein the sulfur-containing nitrogen compound is at least oneselected from pyridinealkanethiols, pyridylalkanethioacetals,aminoalkanethiols and thiazolidines.
 4. The process for producingbisphenol A as claimed in claim 1, wherein the reaction temperaturefalls between 60 and 100° C.
 5. The process for producing bisphenol A asclaimed in claim 1, wherein from 30 to 50% of all acetone to be fed intothe reactor unit is fed into the first reaction zone.
 6. The process forproducing bisphenol A as claimed in claim 1, wherein the liquid hourlyspace velocity (LHSV) in each reaction zone falls between 0.2 and 30hr⁻¹.
 7. The process for producing bisphenol A as claimed in claim 1,wherein the acidic cation-exchange resin catalyst is a sulfonic acidcation-exchange resin.
 8. The process for producing bisphenol A asclaimed in claim 1, wherein the acidic cation-exchange resin is selectedfrom the group consisting of a sulfonated styrene-divinylbenzenecopolymer, a sulfonated crosslinked styrene polymer, aphenol-formaldehyde-sulfonic acid resin, a benzene-formaldehyde-sulfonicacid resin, and mixtures thereof.
 9. The process as claimed in claim 1,wherein the acidic cation-exchange resin is partially neutralized with asulfur-containing nitrogen compound in from 20 to 50% of the acid sites.10. The process for producing bisphenol A as claimed in claim 1, whereinthe sulfur-containing nitrogen compound is 2,2-diniethylthia zolidine.11. A process for producing bisphenol A, comprising: continuouslyfeeding phenol and acetone into a reactor unit having at least tworeaction zones connected in series, and reacting the acetone and thephenol in the presence of an acidic cation-exchange resin, wherein thecation-exchange resin is partially neutralized with a sulfur-containingnitrogen compound present in from 15 to 50% of the acid sites of thecation-exchange resin, and acetone having a methanol concentration offrom 1,000 to 3,000 ppm is separately fed into at least two reactionzones in the reactor unit.
 12. The process as claimed in claim 11,wherein the molar ratio of phenol:(all acetone) is from 6 to
 13. 13. Theprocess as claimed in claim 11, wherein the sulfur-containing nitrogencompound is at least one selected from the group consisting of apyridinealkanethiol, a pyridylalkane thioacetal, an aminoalkanethiol anda thiazolidine.
 14. The process as claimed in claim 11, wherein thereacting is carried out at a temperature of from 60 to 100° C.
 15. Theprocess as claimed in claim 11, wherein from 30 to 50% f the totalamount of acetone fed into the reactor unit is fed into a first reactionzone.
 16. The process as claimed in claim 11, wherein the liquid hourlyspace velocity in each reaction zone is from 0.2 to 30 hr⁻¹.
 17. Theprocess as claimed in claim 11, wherein the acidic cation-exchange resincatalyst is a sulfonic acid cation-exchange resin.
 18. The process asclaimed in claim 11, wherein the acidic cation-exchange resin isselected from the group consisting of a sulfonatedstyrene-divinylbenzene copolymer, a sulfonated crosslinked styrenepolymer, a phenol-formaldehyde-sulfonic acid resin, abenzene-formaldehyde-sulfonic acid resin, and mixtures thereof.
 19. Theprocess as claimed in claim 11, wherein the acid cation-exchange resinis partially neutralized with a sulfur-containing nitrogen compound infrom 20 to 50% of the acid sites.
 20. The process as claimed in claim11, wherein the sulfur-containing nitrogen compound is2,2-dimethylthiazolidine.